"People are not illegal" read the t-shirt.
Clever. Of course nobody thinks people are illegal so the shirt wearer is technically correct. Is anyone claiming that illegal aliens are themselves illegal? No. Rather, it is understood by everyone not inclined to wear a "people are not illegal" t-shirt that said folks are somewhere - in the USA - that they are not legally allowed to enter.
So the clever set are insinuating that, because people are not illegal, that they are then somehow entitled to enter into the US. Just stupid. But they are part of a club that thinks they are clever and passionate and humane and oh so caring while those who disagree are racists etc... I bet that feels good.